Adiponectin is a protein specific for animal adipose tissue first separated from human adipose tissue by Maeda et al. in 1996 (Maeda et al., Biochem. Biophys. Res. Commun., 221:286, 1996). Adiponectin is present in abundance in blood as well as in adipose tissue, being found at a concentration as high as 5 to 10 μg/ml in normal human blood (Arita et al., Biochem. Biophys. Res. Commun., 257:79-83, 1999).
It is known that patients with obesity have a high prevalence of cancer and a reduced concentration of blood adiponectin (Arita et al., supra). Blood adiponectin has been previously shown to have the effects of inhibiting proliferation of monocytes- and B cells (Japanese Patent Laid-Open No. 2000-256208) and suppressing activation of hepatic stellate cells and production of extracellular matrixes (Japanese Patent Laid-Open No. 2002-363094). However, the relationship between blood adiponectin concentration and illness in obese patients has not sufficiently been demonstrated.
Thus, as a result of further advancing an investigation and study relating to the relationship between blood adiponectin concentration and illness, the present invention was completed by discovering that reduced blood adiponectin concentration promotes carcinogenesis.
An object of the present invention is to provide a new anti-tumor agent, in particular, an anti-tumor agent capable of inhibiting carcinogenesis in the liver, use of adiponectin as an anti-tumor agent, and a prophylactic or therapeutic method against a tumor using adiponectin.